Between your Main Deck, Extra Deck and Side Deck, you may only have 3 copies of 1 card of the same name. Here are some examples:

Example 1

"Harpie Queen", on the other hand, only has it's name treated as "Harpie Lady" while it is face-up on the field, or in the Graveyard, but not in the Main Deck, so you can have 3 copies of this card, in addition to any legal combination of the above cards.

  • The rule also applies to "A Legendary Ocean". Its card effect states its name is treated as "Umi" at all times, so you can only have 3 cards in total between these two. You cannot have 3 copies of "A Legendary Ocean" and 3 copies of "Umi" in your deck.

Example 2

  • "Proto-Cyber Dragon" only has its name treated as "Cyber Dragon" while it is face-up on the field. It is not illegal to have 4 or 5 cards on the field that all have the same card name, if the name change is only applicable while on the field and not in the Main Deck. So, you may theoretically have 3 copies of "Cyber Dragon", and 3 copies of "Proto-Cyber Dragon" in your Main Deck. However, Cyber Dragon is Limited for its power, reducing the amount you may have in a deck.

Example 3

In the above cases, a duelist may theoretically have up to 3 of each card above in their Deck. These cards are seen as Retrained from the original Normal Monster or Ritual Monster version of the card

Example 4

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